In this study, an experimental investigation was done to study the behaviour of Normal Strength Concrete (NSC) and High Strength Concrete (HSC) Plain beams under torsion with the concrete mix of M40 and M100. No mineral admixtures are used to obtain the required strength of concrete. Eight NSC beams and eight HSC beams whose width was varying with 75 mm, 100 mm, and 150 mm; depth varying as 75 mm, 100 mm, 150 mm and 200 mm; and span of the beams varying 600 mm, 800 mm and 1200 mm were casted and cured to stud the effect of torsion. The principle aim of this study was to understand the torsional behaviour of the NSC and HSC beams for rotation, cracking, size effect and torsional strength. A standard torsional loading method was used for conducting the testing of beams. The results obtained were compared with different theories and code equations. It was observed that the torsional strength of the beam increases with the increase in strength of concrete. HSC beams have higher torsional strength than the NSC beams which has the same amount of reinforcement.